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Establishing the Target Population

What is a Target Population?

Also see: Relationships among Target Population, Sample Frame, Samples, Sampled Population, Estimates, and Assumptions

Examples - Lakes, Streams, Estuaries


Before the sample survey can be conducted, a clear, concise description of the target population is needed. In statistical terminology the target population (often shortened to "population") does not necessarily refer to a population of people. It could be a population of schools, area units of farm land, freshwater lakes, or the network of streams.  The description of the target population must explicitly identify the aquatic resource of interest and include criteria for determining whether a resource unit is in or out of the target population.  Another way of thinking about target population is that it is the aquatic resource for which quantitative estimates are needed.

For example, if we were conducting a sample survey to estimate the percentage of students at a university who participate in intramural sports, the target population would consist of all the enrolled students. The individual students would be the sampling units, and the registrar's office could provide a list of students to serve as the sampling frame. We could draw a representative (random) sample of students from this list and interview them about their participation in sports. Their responses would be "yes or no." The percentage of interviewed students who participate in intramural sports would yield an estimate of the "true" percentage for all students. 

For a stream survey, the target population might be all perennial, wadeable streams in a watershed. The sampling unit is a point along the stream length, and an associated response design that specifies the measurement protocol and the sampling unit, e.g., electro-shocking with an area 40 times the stream width in length. The response variable might be "degraded" or "non-degraded" based on measures of water quality. Conceptually, the collection of all possible point locations along these streams serve as a sampling frame, similar to the list of students in the previous example.

Lakes - Example

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Streams (Aquatic/Riparian Resource) - Example

Alternative Defining Elements of Stream Target Population

Implications of choice

EMAP Western Pilot Example

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Estuaries - Example

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